The Merriam-Webster dictionary defines the anterior cruciate ligament as "a cruciate ligament of each knee that attaches the front of the tibia with the back of the femur." In the fantasy football dictionary, it's defined as the ligament that wrecks your season. In 2011, five prominent runners went down with the ailment -- Jamaal Charles, Tim Hightower, Knowshon Moreno, Adrian Peterson and Rashard Mendenhall. Of course, the three biggest names on that list are Peterson, Charles and Mendenhall. All were surefire first-round picks in 2011 -- now all three come with huge question marks.

In an effort to better understand the effect of a major knee reconstruction on a runner's immediate future production and value, I went back and looked at seven backs who have suffered ACL ailments since 1999. Taking into consideration their respective ages, the time of the injury and the player's previous workload at the NFL level, there are some definite trends that can be observed. Unfortunately, most of them are bad news when it comes to a back returning to his previous level of production in the first year after such a major operation. Here's the data in full:

Projected totals (full season, 16 games) are based on the per game averages that each player recorded that year before suffering his ACL injury.

Kevin Smith, Lions (2009 - age 23)

Diagnosis: Smith suffered his ACL tear in the 13th game of the 2009 season, so he had a disadvantage in that he was injured late. Smith was an old 23 (if that's possible), too. While he recorded just 455 carries in under two NFL seasons, he also carried the football a ridiculous 450 times in his final collegiate season at Central Florida. Smith missed the first three games of 2010, rushed for 50 or more yards just once before landing on injured reserve with a thumb ailment. He was effective at times in 2011, but Smith's health still made him a risk.

Deuce McAllister, Saints (2007 - age 29)

Diagnosis: McAllister suffered what was his second ACL tear at the NFL level in just the third game of the 2007 season, but he was at a huge disadvantage being 29 and at the end of his career. He returned to play in 13 games during the following year, but McAllister was rarely effective. In fact, he failed to rush for more than 75 yards in a single game while averaging a mediocre 3.9 yards per carry. That's a far cry from his salad days of 2002-03, when McAllister scored a combined 24 touchdowns and was considered a fantasy star as the team's featured back.

Ronnie Brown, Dolphins (2007 - age 26)

Diagnosis: Brown was the best running back in fantasy football in 2007 -- that is, until he blew out his knee in the seventh game of the season. His projected scrimmage yards would have been the 11th-most ever in NFL history at the time, so his was a major loss for fantasy owners. While Brown did play in a full 16 games the following season, his yardage stats paled in comparison to his projected 2007 totals -- he also averaged close to one full yard fewer per carry. The fact that he suffered the ailment before midseason helped, but Brown was never the same again.

Deuce McAllister, Saints (2005 - age 27)

Diagnosis: The first ACL tear of McAllister's pro career came in 2005, when he went down after five games. The fact that McAllister had averaged 21 carries a game in the three previous seasons might have contributed to the ailment, but he came back the following year with relative success. While he averaged close to five fewer carries a game compared to 2002-04, McAllister still rushed for a respectable 1,057 yards and 10 touchdowns. Going down in the first half of the previous season gave him more time to recover, which no doubt helped his overall totals.

Jamal Lewis, Ravens (2001 - age 21)

Diagnosis: Lewis is a unique case, because he suffered his right ACL tear before the start of the 2001 season and missed the entire year. The fact that he was injured so early was a huge advantage for the bruising back, who also tore up his left knee in 1998 as a collegiate player with the Tennessee Volunteers. With youth on his side and a full season off the gridiron, Lewis made a successful return in 2002 with 1,327 yards on the ground and seven total touchdowns. Those weren't huge numbers, however, and again Lewis was a special example in this research.

Edgerrin James, Colts (2001 - age 23)

Diagnosis: James is a prime example of how an ACL reconstruction can kill a back's value the following year. A fantasy star in his prime, James was on pace to post nice totals before blowing out his knee six games into 2001. He did come back to play 14 games the following year, but his production took a nosedive. The fact that he was still young helped James after 2002, as he went on to average a solid 1,437 rushing yards with 34 total touchdowns in the next three years. But clearly, James wasn't the same player in his first year back from the ACL procedure.

Terrell Davis, Broncos (1999 - age 27)

Diagnosis: Davis is the poster child of a running back who suffered from overuse. From 1996-98, he averaged an unbelieveable 368.6 carries a season including 392 in 1998, when he rushed for 2,008 yards. That, ironically enough, is the year before Davis suffered his ACL ailment. Though he did injure it just four games into the season, Davis' workload the previous three campaigns all but doomed him in the latter stages of his career. He played in just five games the following season due to injuries and never rushed for close to 1,000 yards again.

Jamal Anderson, Falcons (1999 - age 27)

Diagnosis: The "Curse of 370" victimized Anderson, who had 410 carries in 1998 before blowing out his ACL in the second game of the 1999 campaign. The fact that he was injured so early in the season did help his recovery and value for the following season, but he still posted mediocre numbers overall. In fact, he recorded 822 fewer rushing yards and 10 fewer total touchdowns compared to his last full season. It also didn't help that Anderson was into his late 20s at the time. He would tear up a knee once again in 2001, which forced him out of football.

ACL Overview

The numbers above make it clear -- the older a running back is at the time of an ACL tear, the worse his chances are to be productive the following season. We have also learned that suffering the ailment early in a season can be an advantage, as it allows more time to rehab and recover. That's the reason I'm not as worried about Charles. While a decrease in production should be expected compared to his 2010 totals, he'll have had far more time than Peterson and Mendenhall to come back. Charles is also just 25 years old, so he clearly has youth on this side.

Mendenhall, who tore up his knee in the Steelers' regular-season finale, will have a long road ahead. The fact that he's young at the age of 24 is an advantage, but he suffered his ACL injury so late that he could be in danger of missing the start of the 2012 campaign. Based on the fact that his numbers were already down compared to his 2010 totals, it's going to be tough to consider the Illinois product more than a low-end No. 2 fantasy runner or flex starter at this point. He could move up a bit as the offseason rolls on, but he's not a No. 1 option.

In the case of Peterson, I think he's going to be hard pressed to be the elite fantasy back he's been -- at least in 2012. Remember, he ripped up his knee in the next to last week of the regular season, meaning he's in danger of landing on the Physically Unable to Perform (PUP) list. When you also consider the huge workload he's endured over the last four years, I'd struggle to build an argument for Peterson being ranked as a No. 1 back in fantasy land next season. Instead, barring setbacks in his rehab, he'll be more of a No. 2 option across the board.